1. Field of the Invention
The present invention relates to an apparatus for detecting pinching of an object of a power window apparatus and, more particularly, to an apparatus for detecting the pinching of an object of a power window for detecting the pinching of an object in accordance with a change in ambient temperature of the power window without using a temperature sensor.
2. Description of the Related Art
Hitherto, in order to prevent an object from being pinched in a window and damaged at the time of window closing operation and prevent an excessive load from being applied to a motor used for opening and closing the windows, a power window apparatus for opening and closing the windows of a vehicle senses the pinching of an object and either stops or reverses the motor when the pinching of an object is sensed, thereby avoiding damaging the object and preventing application of an excessive load to the motor.
A known power window apparatus which senses the pinching of an object comprises at least a motor for opening and closing windows, a motor driving unit for driving the motor, a pulse generator for generating a pulse, a microcomputer control unit (MCU), and an operation switch for opening and closing the windows by manual operation. The pulse generator is coupled to the motor. The microcomputer control unit is connected to the pulse generator, the operation switch, and the motor driving unit. The motor driving unit is connected to the motor.
In the power window apparatus which senses the pinching of an object and has the above construction, when any of switches in the operation switch is operated, a drive signal from the microcomputer control unit is supplied to the motor via the motor driving unit to rotate the motor and allow a window to be opened or closed in accordance with the operated switch. When the motor rotates, the pulse generator coupled to the motor operates and generates a two-phase pulse. The microcomputer control unit acquires a pulse edge interval of the two-phase pulse generated from the pulse generator by counting clock signals and compares the acquired count value as a motor torque value with a base value which is preliminarily set in an internal memory. When the motor torque value is considerably larger than the base value, occurrence of the pinching of an object in the window is determined and the motor is immediately stopped or reversed.
The known power window apparatus which senses the pinching of an object is usually disposed on the inner side of a door panel in a vehicle. A motor torque for opening and closing the window fluctuates according to the ambient temperature when the vehicle is used, that is, the temperature on the inside of the door panel.
FIG. 8 is a characteristic diagram showing an example of the state of fluctuation in the motor torque associated with fluctuation in the ambient temperature of the motor for opening/closing windows.
As shown in FIG. 8, when the ambient temperature is room temperature, for example, within a range from -10.degree. C. to 40.degree. C., fluctuation in the motor torque is small. When the ambient temperature becomes -10.degree. C. or lower, especially about -40.degree. C. or becomes 40.degree. C. or higher, especially about 80.degree. C., the fluctuation in the motor torque becomes considerably large. When the pinching of an object in the window is sensed by using the motor torque at the ambient temperature, a larger error occurs compared to sensing the pinching of an object in the window at room temperature.
In the known power window apparatus which performs a pinching detecting operation, therefore, a correction factor indicative of the relation between the ambient temperature and the motor torque is preliminarily obtained and stored in the internal memory. When the ambient temperature is sensed by the temperature sensor disposed on the inside of the door panel, the correction factor corresponding to the detected ambient temperature is determined from the internal memory. The motor torque value is corrected by using the correction factor, and the pinching of an object in the window is sensed by using the corrected motor torque value.
Since the known power window apparatus which performs the temperature correction senses the pinching of an object in the window according to the ambient temperature of a vehicle which is being used, the apparatus is effective when the ambient temperature fluctuates. The relation between the fluctuation in the ambient temperature and that in the motor torque value is not always a proportional relation. Moreover, the motor torque characteristics of the motor for opening and closing windows largely vary among motors. Even if the motor torque value is corrected in correspondence with the fluctuation in the ambient temperature, an accurate motor torque value dealing with the fluctuation in the ambient temperature cannot be obtained. The error still occurs at the time of sensing the pinching of an object in the window.
The the known power window apparatus in which the temperature correction is performed has a problem in that the ambient temperature sensed by a temperature sensor varies according to the position in which the temperature sensor is disposed. Thus, an accurate motor torque value dealing with the fluctuation in the ambient temperature cannot be obtained and an error occurs at the time of sensing the pinching of an object in the window.